The invention relates to a spinning process and apparatus for carrying out an amine-oxide process according to the dry/wet-spinning process. The spinning apparatus comprises a spinneret having spinning holes for extruding filaments, a container for holding spinning bath liquid, an air gap defined as the distance between the spinneret and the surface of the spinning bath liquid and a shaped body supported in the container of spinning bath liquid for bundling and diverting the extruded filaments.
In general terms, in the dry/wet spinning process, the spinning dope is extruded through a forming tool, such as a spinneret, to form filaments or other shaped bodies. The extruded bodies are then exposed to a non-precipitating medium such as air or an inert gas. In the case of filaments, the filaments are stretched in the air or inert gas medium and subsequently conducted into a spinning bath liquid (precipitation bath), wherein the filaments coagulate.
The amine-oxide process according to the dry/wet-spinning process is known from DE-A -29 13 589. Generally, the amine-oxide process involves the production of cellulose molded bodies using tertiary amine-oxides. According to this process, cellulose is dissolved in a mixture of water and a tertiary amine-oxide to form a solution. N-methylmorpholine-N-oxide (NMMO) is primarily used as the amine-oxide. Other amine-oxides are described in, e.g., EP-A -0 553 070. A process for the production of moldable cellulose solutions is disclosed in EP-A-0 356 419, (U.S. Pat. No. 5,094,690).
WO 93/19230 and WO 95/04173 disclose an advantageous embodiment of the amine-oxide process and a device for the production of cellulose fibers. A solution of cellulose in a tertiary amine-oxide is molded in a hot state, and the molded solution is then introduced through a gaseous medium (air) into a precipitation bath to precipitate the cellulose therein. The hot, molded solution is cooled before it is introduced into the precipitation bath. The cooling is carried out immediately after the molding by blowing air on the molded cellulose filaments in a direction which is generally perpendicular to the direction of travel of the filaments. The process enables the cellulose solution to be spun with a high filament density, while preventing adhesion between the individual filaments after they are extruded from the spinneret.
DD-A -218 121 discloses another dry/wet-spinning process for the production of cellulose fibers from solutions of cellulose in tertiary amine-oxides. The cellulose solution is spun into an air gap, i.e. the space between the spinneret and the surface of the spinning bath liquid, stretched and conducted into an aqueous precipitation bath. According to DD-A - 218 121, the air gap may be reduced without any negative effects on the spinning safety if a polyalkylene ether is added to the cellulose solution before commencement of the spinning operation. The small air gap reduces the risk of adhesion between the freshly extruded filaments.
EP-A-0 574 870 discloses yet another dry/wet-spinning process for processing solutions of cellulose in tertiary amine-oxides and points out the advantage of a small air gap. According to the disclosure, adhesion between the individual filaments during the spinning operation is prevented even though the spinning process employs a small air gap and a high number of spinning holes per area unit, by directing the filaments through a spinning funnel and into the spinning bath liquid. Spinning bath liquid flows through the spinning funnel in a direction parallel to the flow of the filaments. The longitudinal axis of the spinning funnel is substantially vertical, i.e. perpendicular to the plane of the spinneret. The flow of the spinning bath liquid is directed downwards from above and is generated from the gravitational fall of the spinning bath liquid. The drawing or stretching of the extruded filaments is accomplished by the flow of the spinning bath liquid through the spinning funnel.
There are a number of problems associated with the spinning device disclosed in EP-A 0 574 870. First, the small diameter of the spinning funnel sets an upper limit on the number of filaments which can be conducted through the funnel at any one time. This upper limit prevents the device from being used effectively in industrial settings. For example, when employing a diameter of 6 mm, as disclosed in EP-A-0 574 870, it is only possible to conduct a filament bundle consisting of not more than 100 filaments through the funnel since spinning bath liquid also has to flow through the funnel. This limits the spinneret to no more than 100 holes.
When a larger spinneret is used, i.e. one having thousands of spinning holes, such as described in Austrian Patent AT-B 397.392 of the present assignee, the diameter of the funnel pipe must be larger and a greater amount of spinning bath liquid must be discharged through the funnel pipe and circulated in the bath. The heavy flow of spinning bath liquid causes turbulent flows in the spinning bath, thereby interfering with the dry/wet- spinning process.
GB-A-1,017,855 discloses another device having a spinning funnel for dry/wet-spinning of synthetic polymers. Spinning bath liquid flows through the funnel, parallel to the flow of the extruded fibers. The spinneret is located approximately 0.5 cm above the spinning bath surface.
In view of the problems discussed above, it is an object of the present invention to provide a spinning device which achieves "good spinnability" (high spinning safety) without complex equipment. "Good spinnability" is defined as attaining a maximum final drawing as high as possible (minimum titer) before the fiber breaks. Another indicator of "good spinnability" is the period of time during which spinning is possible without the occurrence of spinning deficiencies which require technical assistance. Moreover, even when using spinnerets having high hole densities, the adhesion of the fresh extruded filaments in the air gap is to be prevented, and a titer as constant as possible (low titer variations) is to be attained.
It is another object of the present invention to provide a spinning process and apparatus for a dry/wet spinning process whereby it is possible to perform the process with high spinning safety, simultaneously:
(a) to provide a small drawing space (air gap) and PA1 (b) to use spinnerets having a high hole density and allowing for a high dope throughput.
It is a further object of the invention to provide such spinning process and apparatus in which turbulent flow in the spinning bath is avoided and the apparatus is readily adjustable to accommodate spinnerets of various sizes.